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A class instance is an object-oriented programming (OOP) object created from a class. Each instance of a class shares a data layout but has its own memory allocation.
According to Design Patterns: Elements of Reusable Object-Oriented Software: "Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory method lets a class defer instantiation to subclasses." [2] Creating an object often requires complex processes not appropriate to include within a composing object.
In class-based, object-oriented programming, a constructor (abbreviation: ctor) is a special type of function called to create an object.It prepares the new object for use, often accepting arguments that the constructor uses to set required member variables.
In class-based programming, a factory is an abstraction of a constructor of a class, while in prototype-based programming a factory is an abstraction of a prototype object. A constructor is concrete in that it creates objects as instances of one class, and by a specified process (class instantiation), while a factory can create objects by instantiating various classes, or by using other ...
A class defines an implementation of an interface, and instantiating the class results in an object that exposes the implementation via the interface. [3] In the terms of type theory, a class is an implementation—a concrete data structure and collection of subroutines—while a type is an interface .
In class-based, object-oriented programming, an instance variable is a variable defined in a class (i.e., a member variable), for which each instantiated object of the class has a separate copy, or instance. [1] [2] An instance variable has similarities with a class variable, [3] but is non-static.
Using a factory method to create instances of a class (factory method pattern) Storing the instances in a map, and returning the same instance to each request for an instance with same parameters (multiton pattern) Using lazy initialization to instantiate the object the first time it is requested (lazy initialization pattern)
Alternatively, instantiating a class using the new keyword generates an object with default attribute values. For instance, in the context of designing a system for managing bank account transactions, it may be necessary to duplicate the object containing account information to conduct transactions while preserving the original data.